Typically, pond structures or high-volume tanks are used for raising and sustaining various forms of aquatic life for commercial sales, environmental testing or similar applications which require sustaining large quantities of such life. It is, therefore, generally desirable to ensure that the water in the pond structure, or alternatively in the high-volume tank, be maintained substantially free of organic-based materials, such as excess fish food, excrements and other contaminants which may be damaging to the aquatic life. Several different types of filters and aerators have been developed which have met with varying degrees of success in maintaining the desired water conditions. However, in general these have not proven to be entirely satisfactory, either because they do not have sufficient water circulation capacity, require regular replacement of all of the water in the tank, are expensive to manufacture, costly to operate, difficult to clean, or not suitable for high-volume application.
In most filtering systems, aerobic bacteria are developed on the filter bed or filter element which is designed to destroy waste and purify the water. However, limited circulation of the water in the system causes difficulty in producing an effective and efficient bacterial action which will dispose of the wastes in the water. Thus, in many instances, the filter must be frequently cleaned or replaced.
Many systems have been developed for filtering small-capacity fish tanks like the aquariums found in homes. For example, U.S. Pat. No. 3,722,685 discloses a water pump-induced circulation system, wherein a lower chamber is defined in the bottom of the aquarium tank and has a centrifugal water pump which draws water from the chamber and circulates the water through a filter that is located above the water level for easy access for replacement. The cleansed water, after passing through the filter, is returned to the bottom chamber within the tank. This system is designed for a large capacity pump to draw from the bottom of the tank through the upper exposed filter. Again, with such a system, it is extremely difficult to provide enough oxygen supply into the liquid in the tank to support aquatic life because the oxygen is supplied to the water by absorption at the surface.
To address the above-mentioned problem, systems such as the one disclosed in U.S. Pat. No. 4,817,561 to Byrne et. al. have been developed. Byrne discloses an aeration and filtration system for an aquarium. The system includes a porous filter bed and a pump located in a chamber below the filter bed. The system in Byrne draws oxygen-enriched liquid and oxygen-depleted liquid into the pump chamber and mixes the liquid in that chamber. The oxygen-enriched mixture is then expelled into the fluid environment. The system in Byrne addresses the problem of disposing of materials which may be collected in a filter without frequent filter replacement. Byrne also addresses the problems of providing enough oxygen supply into the liquid in the tank to support aquatic life.
Other more elaborate types of aeration and filtering systems have been developed for raising aquatic life in ponds or in high-volume tanks, such as those disclosed in U.S. Pat. Nos. 3,889,639; 4,221,183 and 5,510,022. However, most of the known prior art systems are costly to manufacture or costly to maintain.